Inter-annual rainfall variability may foster lake regime shifts: An example from Lake Bourget in France

The Intergovernmental Panel on Climate Change anticipates increasing extreme rain events in the 21st century, leading to more frequent floods and more phosphorus transported into lakes, enhancing the risk of their eutrophication. This paper reports research assessing this risk on Lake Bourget in France, by coupling a statistical estimation of annual phosphorus transportation from annual rainfall and a dynamical model estimating the evolution of the phosphorus concentration in the lake in the period 2000-2050 according to yearly phosphorus transportation. The study of the model on the past suggests that the relative drought of the 2000s has fostered the effect of management measures to reduce phosphorus loading, enabling compliance with the Organisation for Economic Co-operation and Development guidance target for 2020. Simulations on different scenarios for the future show that a 10% increase in the rainfall standard deviation nearly doubles the probability of eutrophication, from 2.40% to 4.26% between 2016 and 2050.